Operator site:

Search sites of a Particular Domain

List of Domain Extensions by Wikipedia

These codes can be used with the search operator search term site:.XXX, where XXX is the domain extension to only search websites with that extension.

Here is an example of a search within only educational websites:

Search sites from a Specific Country

Google's Country Codes

These codes can be used with the search operator search term site:XX, where XX is the country code to only search websites from that country.

Here is an example of a search within only Australian websites:

Search a Particular Website

Here is an example of a search of only the SAS website: